Which metabolite signals high energy status and shunts carbon to fatty acid synthesis by inhibiting PDH?

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Multiple Choice

Which metabolite signals high energy status and shunts carbon to fatty acid synthesis by inhibiting PDH?

When energy is abundant, the cell shuts down the entry of pyruvate into the acetyl‑CoA pool and redirects carbon toward storage pathways like fatty acid synthesis. Acetyl‑CoA serves as both the signal of ample energy and the building block for fatty acids, making it the best fit for this role. It inhibits the PDH complex (via feedback and PDH kinase activation) to prevent extra pyruvate from becoming acetyl‑CoA in the mitochondrion, while the acetyl‑CoA that is available is channeled toward cytosolic fatty acid synthesis (through export as citrate and then conversion back to acetyl‑CoA). NADH also signals high energy and can inhibit PDH, but it isn’t the direct substrate for fatty acid synthesis, whereas acetyl‑CoA directly links energy status to lipid biosynthesis.

When energy is abundant, the cell shuts down the entry of pyruvate into the acetyl‑CoA pool and redirects carbon toward storage pathways like fatty acid synthesis. Acetyl‑CoA serves as both the signal of ample energy and the building block for fatty acids, making it the best fit for this role. It inhibits the PDH complex (via feedback and PDH kinase activation) to prevent extra pyruvate from becoming acetyl‑CoA in the mitochondrion, while the acetyl‑CoA that is available is channeled toward cytosolic fatty acid synthesis (through export as citrate and then conversion back to acetyl‑CoA). NADH also signals high energy and can inhibit PDH, but it isn’t the direct substrate for fatty acid synthesis, whereas acetyl‑CoA directly links energy status to lipid biosynthesis.

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